package collections

import (
    "crypto/sha256"
    "encoding/base64"
    "fmt"
    "strconv"
    "strings"

    "math/rand"

    "golang.org/x/crypto/pbkdf2"
)

const Iterations int = 390000
const KeyLen int = sha256.Size

var letters = []rune("123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")

// 输入字符长度，生成随机字符串
func randStr(n int) string {

    b := make([]rune, n)

    for i := range b {
        b[i] = letters[rand.Intn(len(letters))]
    }
    return string(b)
}

// storedHash是查询出来的用户hash, password是输入的密码，进行比较输入是否正确
func GeneratePasswordHash(password string) (string, error) {
    salt := randStr(22)
    hash := pbkdf2.Key([]byte(password), []byte(salt), Iterations, sha256.Size, sha256.New)
    hashBase64 := base64.StdEncoding.EncodeToString(hash)
    result := fmt.Sprintf("pbkdf2_sha256$%d$%s$%s", Iterations, salt, hashBase64)
    return result, nil
}

func VerifyPassword(storedHash string, password string) (bool, error) {
    // 分解 hash 字符串
    parts := strings.Split(storedHash, "$")
    if len(parts) != 4 {
        return false, fmt.Errorf("invalid hash format")
    }

    // 提取迭代次数、盐值、哈希值
    iterations, err := strconv.Atoi(parts[1])
    if err != nil {
        return false, fmt.Errorf("invalid iteration count")
    }

    salt := []byte(parts[2])

    storedHashBytes, err := base64.StdEncoding.DecodeString(parts[3])
    if err != nil {
        return false, fmt.Errorf("invalid hash encoding")
    }

    // 使用 PBKDF2 计算哈希值
    computedHash := pbkdf2.Key([]byte(password), salt, iterations, sha256.Size, sha256.New)

    computedHashStr := string(computedHash)
    storedHashStr := string(storedHashBytes)

    // 比较计算出的哈希与存储的哈希
    if computedHashStr == storedHashStr {
        return true, nil
    }

    return false, nil
}

// func Test() {
//  // hash := `pbkdf2_sha256\$390000$iI5iVFnZMDVmL2L7Bw5nL0$f7O8ArVr1XJoaK/Uwop43GHH1iPy22GygkeWqU2nxU0=`
//  // hash := `pbkdf2_sha256$390000$SDFD21342DSsdf$VCEqR0t7zF0Eyw7s3DiFrfivcT/c4ln9Ov3QjvcwZis=`
//  hash := `pbkdf2_sha256$390000$ZmG3cbHttPh15bJT$PpmdJMB9xkt30xkKsZIU7VpIhok6NT+9K2Z/91LjHrc=`
//  password := "chenhaifeng"

//  valid, err := verifyPassword(hash, password)
//  if err != nil {
//      fmt.Println("Error:", err)
//  } else if valid {
//      fmt.Println("Password is valid!")
//      pwdHash, _ := generatePasswordHash(password)
//      fmt.Println(pwdHash)
//  } else {
//      fmt.Println("Invalid password")
//  }
// }